This invention relates to a transmission system for a marine drive.
In a conventional marine drive, including an engine and a propulsion unit, the engine is directly and mechanically connected to the propeller through a gear box. As a result, the speed of the propeller is directly proportional to the speed of the engine in a ratio established by the gears of the gearbox.
It has been recognized that the usual selection of marine drive characteristics provides unsatisfactory boat performance at low-speed operation, such as for trolling or docking. One mechanism for improving the low-speed performance of the boat is disclosed in my copending patent application Ser. No. 07/096,739 filed Sept. 15, 1987. The structure disclosed in this application provides a fluid coupling apparatus in connection with a series of variable position vanes disposed between the pump and turbine components of the fluid coupling. The vanes are actuable to govern the direction of impingement of fluid on the turbine component of the fluid coupling. The position of the vanes determines the amount of power transferred from the fluid pump to the turbine, to govern the power output of the fluid coupling. The position of the vanes also determines the direction of propulsion of the boat.
The present invention is also directed to a structure for providing improved low-speed operation of a boat. A fluid coupling is provided between the marine drive engine and the gearbox to which the propeller is connected. The fluid coupling includes a rotatable fluid pump connected to the engine and rotatable in response to rotation of the engine crankshaft. A rotatable turbine is driven by the fluid pump. The turbine is connected to a turbine shaft, and is drivingly connected to an output shaft coupled to the propulsion unit for transferring power thereto. A governing means is provided for governing the amount of power transferred from the engine to the propulsion unit. The governing means includes means for varying the amount of power transferred by the output shaft. In one embodiment, the governing means comprises a variable force brake which acts on the output shaft to control its speed of rotation and thereby the amount of power transferred from the engine to the propulsion unit by the output shaft. In order to provide reverse operation of the boat, a series of reactor vanes is provided which is rotatably driven by the fluid pump in a direction opposite to the direction of rotation of the turbine. The reactor vanes are connected to a reactor shaft, which is drivingly connected to the output shaft. Both the turbine shaft and the reactor shaft are provided with a brake mechanism and a clutch mechanism for selectively engaging the respective shafts with the output shaft. In one embodiment, the reactor shaft and the turbine shaft extend from the fluid coupling along a common axis, with one shaft being tubular in cross section and the other shaft extending through the hollow interior of the tube. For forward operation of the boat, a brake is applied to the reactor shaft to maintain it stationary, while the turbine shaft is clutched together with the output shaft to provide rotation thereof and transfer of power from the engine to the propulsion unit, to propel the boat in a forward direction. For reverse operation, a brake is applied to the turbine shaft to maintain it stationary, and the reactor shaft is clutched together with the output shaft to provide rotation thereof and transfer of power from the engine to the propulsion unit to propel the boat in a reverse direction. The variable force brake can be applied to the output shaft, and is capable of overcoming the rotation imparted to the output shaft from either the turbine shaft or the reactor shaft. The variable force brake is operable in response to low-speed boat operation to provide improved brake performance for trolling and/or docking. For high-speed operation where the characteristics of the fluid coupling are undesirable, a clutch is provided to directly connect the fluid pump to the turbine and to thereby eliminate the effect of the fluid coupling.